Method and apparatus for making resistors



May 21, 1957 w. M. KOHRING METHOD AND APPARATUS FOR MAKING RESISTORSFiled April 22, 1954 R M H 4v m E W M Q R m 1. (mm w A L 0? PM 5 M W8 502661 A JoFrzou N.T\ \N .rzuzuau mm L Nw s Q, J/// 7// 3 R W a A Hm xw SF; Q N N m N m W METHOD AND APPARATUS FOR MAKING RESISTORS Wilbur M.Kohring, Lakewood, Ohio Application April 22, 1954, Serial No. 424,857

13 Claims. (Cl. 117-213) In resistor construction involving metallicfilm resistance elements, it is important that the metal be of uniformthickness, and that it be irremovably secure on itsinsulation support.In the case of deposited metal film construction, involving ceramic orporcelain supports, a problem arises as to attainment of high precisionuniform thickness metal film, and a high degree of satisfactory adhesionof the metal film to the ceramic support. I have found that the lattercondition can be outstandingly met if a glazed ceramic or porcelainsupport be. used and if the glaze be softened or fused such that themetal as deposited thereon takes up adhesion by virtue of the especiallyenforced conditions for union such as to determine a certain extent ofbedding penetration instead of a merely superficial contact.Furthermore, I have found that vapor deposition or vacuum deposition ofthe metal to form the film is particularly effective, but the highestdegree of uniformity of deposit requires some particular precautions.Thereby, high precision products can be attained, such as is notpossible with more general procedures. Further advantages and objects ofthe invention will appear from the following description.

To the accomplishment of the foregoing and related ends, said invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawing setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principle of the invention may beemployed.

In said annexed drawing:

Fig. 1 is a vertical sectional view showing an individual unit of amultiple combinational apparatus in accordance with the invention, otherportions of the apparatus being broken away, this section being taken onthe line I, Fig. 2;

and v Fig. 2 is a fragmentary transverse sectional viewtaken on thelineII, Fig. 1. v

In general, the apparatus involves a hermetic scalable chamber 2, themain cover element thereof being securable and removable with respect tothe stationary base plate 3, and through the latter a piping connection4 provides a vacuum of desired extent, being connected to an air-exhaustmeans of any desired or suitable form. Within the chamber 2. is asupport-frame comprising a lower plate 5 and an upper plate 6 preferablyin annular form which are held in permanent spaced relation by rods 7,nuts 8 above and below the respective plates 5 and 6 serving to lock theplates in their position on the support rods. These rods are permanentlysecured below to the chamber foundation plate 3. Mounted through asuitable stuffing box 10 is a shaft 11 driven by suitable motor means atdesired rate of speed, and this shaft has a gear 12 which meshes withpinions 13 mounted on stub shafts 14 in the plate 5, the pinions beingin one -circular row or in concentric rows about the gear as de-Patented May 21, 1957 termined by the size of the apparatus required inany given case. Each pinion stub shaft carries a chuck 15 of desired orsuitable form to coact with an upper chuck 16 which is spring-pressedpreferably, whereby a ceramic blank 17 can be inserted between the twochucks and thus be held for treatment bymetal deposition. The design ofthe chucks 15, 16 may vary, a general satisfactory form involvingconically dished surfaces by which the included ceramic body isautomatically centered. The upper chuck 16 is on the end of the stubshaft 20 which is slidable through the frame plate 6 and has a collar 21whereby a coil spring 24 between the plate 6 and the collar 21 normallyurges the chuck 16 downward against the ceramic blank to be held. Tomake possible the rotation of chuck 16 notwithstanding its associationwith the pressure spring 24, for instance the stub shaft 20 may be intWo sections, the lower rotating on the upper, while the spring 24-bears stationarily against the plate 6 and the collar 21. For chargingthe apparatus, the cover member 2, which is usually of thick glass, isremoved from the base plate 3, and the glazed ceramic blanks arepositioned between the chucks 15 and 16. Manipulation of the chuck is asimple matter, it being raisable by grasping the flange top 23 andlifting against the spring 24, while the ceramic blank is inserted firstin the lower chuck 15, and then the upper chuck is allowed to springdown into engagement with the upper end of the blank.

An important feature is the provision of a plurality of wires 25spacedly about the ceramic blank 17 in number two and up as appropriateto the size of blank being treated. These wires are held in suitablesupport means and are supplied by controllable current, and they effecta twofold function. In the first place, with current supply they becomeheating elements which heat and soften the glaze on the ceramic blanks.Then, by suitable increase of current, metal may be vaporized off fromthem, under the high vacuum of the vacuum chamber, and the metal vapordeposits on the ceramic blanks as rotated by the pinions 13. The wiresmay be of convenient size consistent with their heating by resistance,and for instance may be .030-.04(l in. The material of the wires 25 ischosen in accordance with the particular resistance metal film desiredon the ceramic cores 17. Thus, one desirable composition is an :20nickelchromium alloy. Other metals which may be used are substantiallypure nickel, alloys such as Constantan, Nichrome, etc. The ends of thewires extend through insulating bushings 27 in the plates and are heldin binding posts 37 supported on the flanged end of the insulatingbushings on the upper side and the lower side of the respective plates 5and 30. Binding screws 3i in each post hold the ends of the wires andthe binding posts are elongated so that each except at the inlet servestwo wires and acts also as a series connector between wires. Where thecurrent supply is for instance 220 or 440 volts the wires are connectedin circuit in series, and depending upon the overall size of theapparatus there may be one or more series circuits therefor. The bindingpost elements serving two Wires, are appropriately positioned on theupper plate and then the lower plate, etc., as required, and with theentry supply line 40 from the current control means 42 through aninsulating bushing 41 in the base 3, the end of such conductor wirepositions alongside the wire 25 in the same binding post opening and theclamping screw 31 then holds both. At the top of the upper plate 30 thecrossover binding post means 37 serially connects to the next Wire, andthis in turn at the bottom connects through another binding post meansto the nextwire, and the latter in turn connects at the top platethrough another binding post means to the next wire, and so on throughall of the wires, and thence out by the exit line not shown. The plate30 is a floating plate supported by stubs 33 which project from the.plate upward through openings in the frame-plate 6, such that thefloating plate 30 with all its connecting wires is normally tensionedupwardly by coil springs 34 between the frame-plate 6 and the head ofthe stubs, such head being a washer and an adjustable nut 35 threaded onthe stub for adjusting the spring tension. This arrangement gives aconstant tension positioning of the wires, irrespective of expansion andcontraction conditions undergone by them in heating and cooling cycles.The plate 30 in its movements is guided by its openings sliding on thesupport rods 7.

In case a wire 25 breaks, damage is prevented by the provision of aninsulation plate 38, of native mica or suitable material, and respectiveopenings allow the passage of wires therethrough, but if the wire breaksit cannot tangle disastrously with other elements. The plate 38 is heldbetween nuts 39 on the support rods 7.

The manner of operation is understood from the foregoing. With the topmember 2 off of the base 3, glazed ceramic blanks 17 are insertedbetween the chucks 15, 16, the latter being raised for this by manuallylifting the fianged head 23 against the spring pressure 24. Wires of thedesired resistance metal are inserted in the binding posts 37, and aresecured by the binding screws 31. The cover section 2 is replaced andsecured on the base plate 3, and the vacuum draw-off is started, andbrought to the desired extent for metal deposition and it is advisableto hold for five minutes after reaching that point before applyingmetal-vaporizing current. The vacuum deposition technique per se followsthe known technique (for instance as in Vacuum Technique by Sol Dushman,pub. John Wiley & Sons, Inc., 1949, pages 757-764) a vacuum of extentsufficient for the metal vapor deposition being applied, but the presentprocedure has the further feature that electric'current is applied tothe wires 17 first such as to heat and soften the glaze of the ceramicblanks, the amperage for this being for instance 4-6.5 depending on thewire size. Then, after the glaze is fused, the current is stepped up toan amperage of 8-12, and under the vacuum which is being applied, metalis vaporized freely from the wires, and deposits on the surface of thesoftened glaze. The ceramic blanks 17 are meanwhile being rotated by thedrive through the pinions 13 and gear 12.

While in the drawing, the number of heating wires 25 surrounding eachceramic blank is illustrated as five, it will be understood that thenumber depends in one respect on the size of blanks and can be of anyworkable order more than two. It will be understood that the size of theblanks may be in accordance with the ultimate products to be turned out,and with large diameter blanks there are of course relatively fewerchucks and their operating pinions. The rate of rotation of the blanksin general may be for instance lVz-Z during the metal vaporizing part ofthe operation, it being seen that to some extent this is dependent uponthe number of heating wires spaced around each blank, and the workingtemperatures selected during the glaze-softening operation and in thevaporization heating, and the thickness of coat desired.

It is seen that metal deposited in the present process is not a mereindependent film on the surface of a ceramic body, but by reason of thefirst softening or fusing of the glaze the metal beds into union suchthat it cannot be scraped or cut ofi.

As an example. Rod-form glazed ceramic blanks, which may have severalspaced circumferential groovings to facilitate ultimate severence into aplurality of finished units, are inserted in the chuck-holders and withwires of 80:20 nickel-chromium positioned in their binding posts, thecover member'2 is set into position, with a gasket, and suitably sealed,and vacuum draw-off is put on, reducing the pressure to about 3 1O" mm.Hg,-and electric cutrent is supplied through the wires to the extent ofabout 5.5 amperes, for the stage of heating and softening the glaze onthe ceramic blanks. Then, after making sure of the minimum vacuum,holding it for five minutes more, the current is increased to about 9amperes, and the vaporization from the nickel-chromium wires proceeds.Meanwhile, the pinions have been rotating the blanks such that they arein constant motion in exposure to the wires. The desired film of metalhaving been deposited on the surface of the ceramic blanks, the vacuumis released, and the cover member removed, and the coated blanks aretaken out of the apparatus.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

I therefore particularly point out and distinctly claim as my invention:

1. In resistor manufacture, the steps of simultaneously rotating each ofa plurality of glazed ceramic blanks before spaced-around wires ofdesired metal and supplying current to the wires first suflicient toheat and soften the glaze on the blanks, and then increasing the currentto vaporize metal from the wires such as to deposit on the soften glaze,while subjecting all to a vacuum.

2. In resistor manufacture, the steps of simultaneously rotating each ofa plurality of glazed ceramic blanks before spaced-around wires ofdesired metal and supplying current to the wires and heating andsoftening the glaze on the blanks, and then vaporizing metal from thewires to deposit on the softened glaze, while subjecting to a vacuum.

3. In resistor manufacture, the steps of simultaneously rotating each ofa plurality of glazed ceramic blanks before spaced-around wires ofdesired metal and supplying current to the wires and heating andsoftening the glaze on the blanks, and then depositing vaporized metalon the softened glaze, while subjecting to a vacuum.

4. In resistor manufacture, the steps of rotating a glazed ceramic blankbefore spaced-around wires of desired metal and supplying current to thewires, and heating and softening the glaze on the blanks, and thenincreasing the current and vaporizing metal from the wires to deposit onthe softened glaze, while subjecting to a vacuum.

5. In resistor manufacture, the steps of rotating a glazed ceramic blankbefore spaced-around wires of desired metal and supplying current to thewires, and heating and softening the glaze on the blank, and thenvaporizing metal from the wires to deposit on the softened glaze,whilesubjecting to a vacuum.

6. In resistor manufacture, the steps of rotating a glazed ceramic blankand applying heat thereto to soften the glaze, and then supplyingdesired vaporized metal to deposit on the softened glaze, whilesubjecting to a vacuum.

7. Apparatus for resistor manufacture comprising a chamber, means forproviding vacuum therein, framing in the chamber including lower andupper plates, a drive shaft from outside into the chamber and having agear, a plurality of pinions about said gear each having anarticle-holding chuck, a plurality of electric heating wires spacedabout each chuck and article therein and held above and below to saidplates so as to extend therebetween, an'insulation guard-plate betweensaid upper and lower plates and having openings for the wires, means fortensioning the wires including spring-suspension of the upper plate, andcurrent-control means for supplying one current range to the wires forheating blanks in the article-holding chucks and another current rangefor vaporizing metal of the wires.

8. Apparatus for resistor manufacture comprising a chamber, means forproviding vacuum therein, framing in the chamber including lower andupper plates, a drive shaft from outside into the chamber and having agear, a plurality of pinions about said gear each to carry an article, aplurality of electric heating wires spaced about each chuck and articletherein and held above and below to said plates so as to extendtherebetween, an insulation guard-plate between said upper and lowerplates and having openings for the wires, means for tensioning the wiresincluding spring-suspension of the upper plate, and current-controlmeans for supplying one current range to the wires for heating blankscarried by the pinions and another current range for vaporizing metal ofthe wires.

9. Apparatus for resistor manufacture comprising a chamber, means forproviding vacuum therein, framing in the chamber including lower andupper plates, a drive shaft from outside into the chamber and having agear, a plurality of pinions about said gear, each to carry an article,a plurality of electric heating wires spaced about each article socarried and held above and below to said plates so as to extendtherebetween, means for tensioning the wires including spring-suspensionof the upper plate, and current-control means for supplying one currentrange to the wires for heating blanks carried by the pinions and anothercurrent range for vaporizing metal of the wires.

10. Apparatus for resistor manufacture comprising a chamber, means forproviding vacuum therein, framing in the chamber including lower andupper plates, a drive shaft from outside into the chamber driving apinion for holding an article, a plurality of electric heating wiresspaced around such article, the Wires being held above and below to saidplates so as to extend therebetween, an insulation guard-plate betweensaid upper and lower plates and having openings for said wires, meansfor tensioning the wires including spring-suspension of the upper plate,and current-control means for supplying one current range to the wiresfor heating the article carried by said pinion and another current rangefor vaporizing metal of the wires.

11. Apparatus for resistor manufacture comprising a chamber, means forproviding vacuum therein, framing in the chamber including lower andupper plates, a drive shaft from outside into the chamber and driving apinion to rotate an article, a plurality of electric heating elementsspaced about the article so carried, said wires being held above andbelow to said plates so as to extend therebetween, means for tensioningthe wires including spring-suspension of the upper plate, andcurrent-control means for heating the wires to vaporization temperature.

12. Apparatus for resistor manufacture comprising a chamber, means forproviding vacuum therein, framing in the chamber including lower andupper plates, :1 drive shaft from outside into the chamber and rotatingan article, a plurality of electric heating wires spaced about sucharticle adapted to be heated to vaporization temperature, said wiresbeing held above and below to said plates so as to extend therebetween,and means for tensioning the wires including spring-suspension of theupper plate.

13. Apparatus for resistor manufacture comprising a chamber, means forproviding vacuum therein, framing in the chamber including lower andupper plates, a drive shaft from outside into the chamber for rotatingan article, wire means extending between said lower and upper plates towhich such article is exposed, means for heating the wire tovaporization temperature and means for tensioning said wire.

References Cited in the tile of this patent UNITED STATES PATENTS2,260,471 McLeod Oct. 28, 1941 2,398,382 Lyon Apr. 16, 1946 2,408,614Dimmick Oct. 1, 1946 2,453,801 Mattern NOV. 16, 1948 2,456,241 Axler eta1. Dec. 14, 1948 2,532,971 Van Leer et a1. Dec. 5, 1950 2,624,823 LytleJan. 6, 1953

1. IN RESISTOR MANUFACTURE, THE STEPS OF SIMULTANEOUSLY ROTATING EACH OFA PLURALITY OF GLAZED CERAMIC BLANKS BEFORE SPACED-AROUND WIRES OFDESIRED METAL AND SUPPLYING CURRENT TO THE WIRES FIRST SUFFICIENT TOHEAT AND SOFTEN THE GLAZE ON THE BLANKS, AND THEN INCREASING THE CURRENTTO VAPORIZE METAL FROM THE WIRES SUCH AS TO DEPOSIT ON THE SOFTEN GLAZE,WHILE SUBJECTING ALL TO A VACUUM.